The invention relates to an apparatus for imprinting images on an endless foil such that they are disposed on a section of predetermined length L by a printing device through which the foil is continuously moved, as the endless foil is directed to a transport element, which divides the foil into the sections of the predetermined length and after which the endless foil is cut into sections of the predetermined length L. The print images need to be accurately disposed within the limits between two adjacent sections of the endless foil and the printing device is activated individually for the printing of each printing image when the length of the endless foil between a section limits generated by the last sectioning and the printing device is a predetermined multiple of the predetermined length L. A buffer arrangement for the endless foil is also provided.
An endless foil printing apparatus is known for example from Applicant's U.S. Pat. No. 5,964,151.
The known apparatus is preferably used when so-called blister packs, in which for example pills are disposed, are to be provided with accurately positioned print images. The pills are always disposed in pockets of a deep drawn blister foil of plastic or paper which are sealed by a cover foil. The cover foil is provided with a print image for the identification of the pills including data regarding the use of the individual pills. It is therefore important that the data are accurately located on the cover foil in accordance with the location of the pills or respectively, the corresponding pockets. Any mismatch between the position of the blister foil and the cover foil should be minimal that is there should be no noticeable mismatch.
With the known apparatus the cover foil can be applied to the blister foil with high accuracy. This is achieved essentially by the fact that the beginning of a foil section to be imprinted is constantly re-determined. By the constant redetermining of the beginning of the section to be imprinted errors are not added up. As a result, even relatively large deviations are generally not detrimental since a deviation in one section does not affect the position of the printing image on the next section. Also, slippage of the foil does not affect the subsequent image positions.
The known apparatus is particularly advantageous if the sections are removed from the apparatus in a discontinuous manner, since the signal activating the printing device to imprint only a single image is generated by a sensor when a compensation roller is disposed in a predetermined position. With the discontinuous removal of the imprinted foil, the compensation roller moves a certain distance along a given path, that is, its position changes dependent on the length of the foil between the printing device and the removal device so that the compensation roller is very suitable for generating a foil length-dependent signal.
If a foil is to be removed from the apparatus in a continuous manner, the apparatus covered by Applicant's earlier patent is not suitable. With the continuous removal of the foil the locations of the section limits move constantly so that the position of the compensation roller cannot be used as a measure for the length of the endless foil between the printing device and the section limit provided by the respective last sectioning.
It is therefore the object of the present invention to provide an apparatus in which the printing images are accurately individually located on an endless foil even if the foil is continuously removed from the apparatus.